A car raised on a two-post lift in the workshop.

There is a knocking noise over speed bumps

A knock over a bump is free play: something in the suspension or steering that should be held tight has enough movement in it to make a noise when the wheel travels. On the roads here that is a component wearing out rather than a fault that appeared overnight — heat and the endless expansion joints work rubber bushes hard. The list of things that knock is short, but every item on it sounds the same from the driver’s seat: drop links and anti-roll bar bushes, control arm bushes, top mounts, worn shock absorbers, and, less often, a track rod end or a loose subframe bolt. They are separated by loading each joint with the weight off the wheel, not by listening.

Can I keep driving it?

Drivable, but do not leave it

Most knocks are a comfort problem first and a safety one later, and a single light knock over a sharp bump is not a reason to stop driving. What changes that is steering: if the knock comes with vague or wandering steering, a clunk when you turn the wheel at low speed, or a tyre that has started wearing on one edge, that is a joint with play in the steering path and it should be looked at promptly.

How we find out which one it is

Shock absorbers, arms, bushes, joints and steering — found by hand on a lift, not by guesswork.

  1. 01

    We reproduce it on the road first

    A noise over bumps, a noise on lock and a noise that rises with speed are three different faults. We drive the car over the surface you described before it goes on the lift, because a suspension fault found only by feel on a ramp is half a diagnosis.

  2. 02

    Every joint is loaded by hand

    Play does not show itself on a part that is standing still and only looked at. It shows when the joint is levered under load. That is what we do to each one in turn, until the knock belongs to a specific component rather than to the front of the car in general.

  3. 03

    We separate noise from unsafe

    A split anti-roll bar bush is a noise. A worn lower ball joint is a safety item. Both go on the report, marked differently, with the reason written next to each, so you are spending on what actually needs it.

  4. 04

    Geometry after the work, not before

    Replacing an arm, a ball joint or a track rod end changes the wheel angles, so the geometry has to be reset afterwards or the new part will eat a tyre. We will tell you plainly whether that alignment is done here or somewhere we send you, before you book, not after.

The job that investigates this: Suspension and steering

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